Studies are aimed at determining whether phospholipase A (PL-A) of microbial origin can influence the presence of prostaglandins (PG) in periodontal disease by providing PG precursors in the gingival crevice and periodontal pockets. Phospholipase A produced by plaque microorganisms will be purified and characterized. Purified preparations will be used to demonstrate their ability to release PG precursors from gingival fragments in vitro and for their potential to produce histopathological changes in tooth supporting tissues after subgingival injections into experimental animals. Microorganisms obtained from pockets of individuals with various periodontal syndromes will be screened to determine whether they can synthesize PG-like substances if provided with the proper precursors. This screening will be performed by following the conversion of 3H-arachidonate to substances that cochromatograph with known PG's. Both PL-A and PG-like substances of bacterial origin will be assessed for their ability to promote fetal bone resorption in vitro.